Rare-earth-doped-fiber light sources (FLS) are commonly used in interferometric fiber optic gyroscopes (IFOG) because of their high optical power, broad optical bandwidth, and high mean wavelength stability. There is an increasing demand for a small size, low weight IFOG to operate in radiation environments. As defined herein, a “radiation environment” is an environment including one or more of high energy particles (such as alpha particles) and high frequency radiation (including, but not limited to, X-rays and gamma rays) from sources such as a nuclear bomb, a nuclear reactor, the sun, or other extra-terrestrial radiation sources. The light propagating within a FLS and an IFOG is referred to herein as “light”, “optical beam”, or “optical pump beam”. Although such optical beams are electro-magnetic radiation, the terms “light”, “optical beam”, and “optical pump beam” as used herein are not the radiation generated by high energy particles, the sun, and nuclear events.
Designing FLS to retain the above mentioned desired properties in a radiation environment is important. However, it is difficult to achieve high wavelength stability of a FLS under radiation. When an IFOG uses an FLS with an unstable wavelength, the IFOG scale factor stability is degraded through mean wavelength change and angle random walk is degraded through bandwidth reduction. In addition, radiation from high energy particles and/or high frequency radiation increase the loss within the whole gyro optical circuit. This power loss leads to a substantial reduction of the optical power at the rate detector of the IFOG, which also degrades the IFOG performance.
It is known in the art that it is possible to reduce the mean wavelength sensitivity of rare-earth-doped-fiber light sources (FLS) to radiation by narrowing the bandwidth of the fiber light source. However, this sacrifices the bandwidth of the FLS, and also reduces the efficiency of the rare-earth-doped-fiber light sources (FLS) in converting pump laser power to FLS output power. For IFOG applications, a wider bandwidth is better. For example, it is desirable for an optical signal coupled to an IFOG to have an approximately 40 nm bandwidth.